Within large photonic networks, such as those used to facilitate optical communications, it is necessary to monitor the performance of individual switching nodes to determine if the control parameters (i.e., control voltages) associated with each node require adjustment. It is critical that such control parameters be maintained within prescribed limits to insure the proper operation of the overall network. This monitoring is particularly important for switching and sub-systems which exhibit an analog switching response (a continuous switching curve with a finite slope between the "on" and "off" switching states). Solid-state guided-wave voltage-controlled directional couplers, such as those based upon lithium-niobate and indium-phosphide architectures, are one type of sub-system with this type of switching response. In addition, such solid-state devices are particularly susceptible to performance fluctuations resulting from thermal variations, aging, etc., increasing the need for performance monitoring.
Previously, the monitoring of control parameters for such optical switches and sub-systems was performed manually on a node-by-node basis using methods which caused an interruption in signals passing through the particular node being tested. This method is impractical for maintaining a large network. Ideally, in a large network it would be desirable to effect such performance monitoring on an automatic basis, and in a fashion which does not interfere with the transmission of the primary optical signals carried over the network.